I’m not receiving notifications

Make sure that sync is on for your device.
On many Android devices, you can turn off sync for all apps at once. Often there is a sync icon that turns sync on and off. You may have turned off sync on purpose or by accident.

Make sure that Gmail sync is on.
In the Gmail app, touch the menu .

Touch Settings.

Choose your account, then make sure the box next to Sync Gmail is checked.

Verify your settings.
Review the steps in the previous section to make sure you have all the right boxes checked.